Upontheirshoulders - That is the staves which went through the rings rested on their shoulders, but the ark itself rested on the staves like a sedan on its poles.
Wise and good men may be guilty of oversights, which they will correct, as soon as they are aware of them. David does not try to justify what had been done amiss, nor to lay the blame on others; but he owns himself guilty, with others, of not seeking God in due order